Cisco Systems C819HG4GVK9 Placing a Low-Speed Serial Interface in Constant-Carrier Mode, 8-17

Chapter 8 Configuring the Serial Interface

How to Configure Serial Interfaces

4.The DCE transitions to the wait DCD drop delay state. This state causes a time delay between the transmission of the last frame and the deassertion of DCD in the controlled-carrier mode for DCE transmits.

5.When the timer expires, the DCE deasserts DCD and transitions back to the ready state and stays there until there is a frame to transmit on that interface.

As shown in Figure 6, the half-duplex DCE receive state machine idles in the ready state when it is quiescent. It transitions out of this state when the DTE asserts RTS. In response, the DCE starts a timer based on the value specified using the cts-delaycommand. This timer delays the assertion of CTS because some DTE interfaces expect this delay. (The default value of this timer is 0 ms; use the half-duplex timer cts-delayinterface configuration command to specify a delay value.)

Figure 6 Half-Duplex DCE Receive State Machine

When the timer expires, the DCE state machine asserts CTS and transitions to the receive state. It stays in the receive state until there is a frame to receive. If the beginning of a giant frame is received, it transitions to the in giant state and keeps discarding all the fragments of the giant frame and transitions back to the receive state.

Transitions back to the ready state occur when RTS is deasserted by the DTE. The response of the DCE to the deassertion of RTS is to deassert CTS and go back to the ready state.

Placing a Low-Speed Serial Interface in Constant-Carrier Mode

To return a low-speed serial interface to constant-carrier mode from controlled-carrier mode, use the following command in interface configuration mode.

SUMMARY STEPS

1.no half-duplex controlled-carrier

DETAILED STEPS

	Command or Action	Purpose
Step 1	no half-duplex controlled-carrier	Places a low-speed serial interface in
		constant-carrier mode.
	Example:
	Router(config-if)# no half-duplex controlled-carrier

	Cisco 819 Series Integrated Services Routers Software Configuration Guide
OL-23590-02		8-17